Field of the Invention
The invention relates to an installation for supplying a fluid such as gas under pressure to pressure medium-actuated or operated systems of a printing machine, and more particularly to a pneumatic pressure supply installation for a printing machine and sub-units disposed upstream and downstream thereof.
It is known in the context of printing machines to perform a variety of operations by means of pressure medium actuated systems. For instance, a pressure supply installation serves to feed pneumatic operating cylinders, pumps for ink and damping medium and compressed air and suction devices.
A simple installation includes at least a compressor, a pressure tank supplied by the compressor, and a network or ring line, at which various users at the individual printing units, at the feeder and at the delivery are connected via valves. When the number of printing units and of the upstream and downstream sub-units is increased, the number of users of the pressure medium and the number of leaks increases. In that case, compressors and tanks must be adapted to the increased air pressure demand. They must be configured accordingly large with respect to operating power and storage capacity.
Compressors with high power output and tanks with high storage capacity are expensive. Starting at a defined threshold value which is defined as the product of pressure and volume, pressure storage tanks require monitoring, so that further costs are incurred for operating the installation. It is furthermore structurally disadvantageous to dimension the compressor and the tank, corresponding to the number of users, for each printing machine to an optimal characteristic magnitude. The requirement would be for a diversity of compressors and tanks, which is detrimental in terms of expedient manufacture.
The pressure medium requirements at a printing machine are subject to strong deviations over time. For instance, if pneumatic elements at printing machines are only used in adjustment fuctions and automation devices, but not during the actual printing operation, then the pressure medium demand is very high during short time periods and virtually zero during long time periods. This, if leakage losses are neglected. Systems with continuous pressurized air production are thus not suitable in printing machines due to their low degree of efficiency. German published, non-prosecuted application DE-OS 20 47 960 describes a control device for a constant pressure hydraulic installation. Several pressure tanks are charged to respectively different pressure levels by a constant pump connected to the input side. Switching valve configurations are connected downstream on the output side of the pressure tanks. Users may be switched to communicate with a specific pressure tank in dependence of the load on the users. With this hydraulic configuration it is possible to supply each of the parallel-connected users with pressure from that pressure tank which corresponds to the actual load condition. It is disadvantageous in that solution that the pressure tanks have different pressures. It is either necessary to provide machine-type containers corresponding to the specifically required pressures, or one must settle on a certain container size configured to a maximum pressure. The feeding of the containers is effected through pressure-controlled 4/3-way valve configurations which, when a threshold value is attained, are switched to the pressure of the respective container. The supply of the container and the user is effected independently from the control of the system with which the user is associated.
In the apparatus for controlling the pressure air supply from a compressor to several air pressure tanks in a pneumatic installation described in German published, non-prosecuted application DE-OS 15 03 415, check valves are provided between the compressor and the pressure air tanks. The check valves are located in the drive chamber of a pressure regulator and they are actuated by pressure differences. They function as nonreturn valves for the pressure air tanks and for a compensating chamber into which the compressor feeds directly. A control of the check valves in dependence on signals from the system in which the users are disposed which are connected to the pressure air tanks is not provided in that solution.
A pressure supply device in users according to German document DE 33 00 493 A1 includes a control device for a valve configuration. When the pressure at a second user has dropped below a given threshold the control device actuates the valve device and returns the same after a short time period. In this way, a pressure chamber is alternatively switched in accordance with predetermined conditions at the second user to a pressure source or to a reservoir. In that solution, two separate pressure media are provided for the supply of the two users, which pressure media are separated by means of a medium transfer carrier, whereby the supply device subsists with only one pressure source with a pump. It is thereby disadvantageous that the first user is directly supplied by the pump, so that the pump must continuously operate and that the separation of the two supply circuits causes high expenditure.